CNR Institute for Photonics and Nanotechnologies

Roma, Italy

CNR Institute for Photonics and Nanotechnologies

Roma, Italy
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Longhi S.,CNR Institute for Photonics and Nanotechnologies
Optics Letters | Year: 2015

Dynamical localization, i.e., the absence of secular spreading of a quantum or classical wave packet, is usually associated with Hamiltonians by the pure point spectrum, i.e., with a normalizable and complete set of eigenstates. Such systems always show quasi-periodic dynamics (recurrence). Here, we show, rather counter-intuitively, that dynamical localization can be observed in Hamiltonians with an absolutely continuous spectrum, where recurrence effects are forbidden. An optical realization of such a Hamiltonian is proposed based on beam propagation in a self-imaging optical resonator with a phase grating. Localization without recurrence in this system is explained in terms of pseudo- Bloch optical oscillations. © 2015 Optical Society of America.


Longhi S.,CNR Institute for Photonics and Nanotechnologies
Optics Letters | Year: 2016

Parity-time (PT) symmetry is one of the most important accomplishments in optics over the past decade. Here the concept of PT mode-locking (ML) of a laser is introduced, in which active phase-locking of cavity axial modes is realized by asymmetric mode coupling in a complex time crystal. PT ML shows a transition from single- to double-pulse emission as the PT symmetry breaking point is crossed. The transition can show a turbulent behavior, depending on a dimensionless modulation parameter that plays the same role as the Reynolds number in hydrodynamic flows. © 2016 Optical Society of America.


Conte S.D.,CNR Institute for Photonics and Nanotechnologies
Nature Physics | Year: 2017

The influence of Mott physics on the doping–temperature phase diagram of copper oxides represents a major issue that is the subject of intense theoretical and experimental efforts. Here, we investigate the ultrafast electron dynamics in prototypical single-layer Bi-based cuprates at the energy scale of the O-2p → Cu-3d charge-transfer (CT) process. We demonstrate a clear evolution of the CT excitations from incoherent and localized, as in a Mott insulator, to coherent and delocalized, as in a conventional metal. This reorganization of the high-energy degrees of freedom occurs at the critical doping pcr ≈ 0.16 irrespective of the temperature, and it can be well described by dynamical mean-field theory calculations. We argue that the onset of low-temperature charge instabilities is the low-energy manifestation of the underlying Mottness that characterizes the p < pcr region of the phase diagram. This discovery sets a new framework for theories of charge order and low-temperature phases in underdoped copper oxides. © 2017 Nature Publishing Group


Longhi S.,CNR Institute for Photonics and Nanotechnologies
Optics Letters | Year: 2015

A method for realizing asymmetric (one-way) transmission of discretized light in modulated, linear, and purely passive optical lattices is suggested, which exploits the idea of unidirectional coherent perfect absorption. The system consists of a linear photonic lattice of coupled resonators or waveguides, side coupled to a chain of lossy elements, in which light can avoid the occupation of the dissipative sites when propagating in one way, but not in the opposite one. Non-reciprocity requires modulation of the resonator/waveguide parameters, realizing a dissipative optical Aharonov-Bohm diode with non-reciprocal behavior. © 2015 Optical Society of America.


Longhi S.,CNR Institute for Photonics and Nanotechnologies
Optics Letters | Year: 2015

Supersymmetric (SUSY) optical structures provide a versatile platform to manipulate the scattering and localization properties of light, with potential applications to mode conversion, spatial multiplexing, and invisible devices. Here we show that SUSY can be exploited to realize broadband transparent intersections between guiding structures in optical networks for both continuous and discretized light. These include transparent crossing of highcontrast- index waveguides and directional couplers, as well as crossing of guiding channels in coupled resonator lattices. © 2015 Optical Society of America.


Longhi S.,CNR Institute for Photonics and Nanotechnologies
Optics Letters | Year: 2015

In quantum mechanics, the space-fractional Schrödinger equation providesanatural extension of the standard Schrödinger equation when the Brownian trajectories in Feynman path integrals are replaced by Levy flights. Here an optical realization of the fractional Schrödinger equation, based on transverse light dynamics in aspherical optical cavities, is proposed. As an example, a laser implementation of the fractional quantum harmonic oscillator is presentedin which dual Airy beams can be selectively generated under off-axis longitudinal pumping. © 2015 Optical Society of America.


Longhi S.,CNR Institute for Photonics and Nanotechnologies
Optics Letters | Year: 2014

We suggest a method for trapping photons in quasi-one-dimensional waveguide or coupled-resonator lattices, which is based on an optical analogue of the Aharonov-Bohm cages for charged particles. Light trapping results from a destructive interference of Aharonov-Bohm type induced by a synthetic magnetic field, which is realized by periodic modulation of the waveguide/resonator propagation constants/resonances. © 2014 Optical Society of America


Longhi S.,CNR Institute for Photonics and Nanotechnologies
Optics Letters | Year: 2014

This Letter shows that bound states in the continuum (BIC), which are normalizable modes with energy embedded in the continuous spectrum of scattered states, exist in certain optical waveguide lattices with PT -symmetric defects. There are two distinct types of BIC modes: BIC states that exist in the broken PT phase, and correspond to exponentially localized modes with either exponentially damped or amplified optical power; and BIC modes with sub-exponential spatial localization that also can exist in the unbroken PT phase. These two types of BIC modes at the PT symmetry breaking point behave differently: in the former case, spatial localization is lost and the defect coherently radiates outgoing waves with an optical power that linearly increases with the propagation distance; in the latter case, localization is maintained and the optical power increase is quadratic. © 2014 Optical Society of America.


Longhi S.,CNR Institute for Photonics and Nanotechnologies
Optics Letters | Year: 2013

A method to realize effective magnetic fields for photons in square lattices of coupled optical waveguides or resonators is suggested, which is inspired by an optical analogue of photon-assisted tunneling of atom optics. It is shown that an artificial magnetic field can be achieved by application of an index gradient and periodic lumped phase shifts or modulation of the propagation constants/resonances, without the need to modulate the coupling strength. © 2013 Optical Society of America.


Longhi S.,CNR Institute for Photonics and Nanotechnologies
Optics Letters | Year: 2013

Zak phase, that is, the Berry phase acquired during an adiabatic motion of a Bloch particle across the Brillouin zone, provides a measure of the topological invariant of Bloch bands in one-dimensional crystalline potentials. Here a photonic structure, based on engineered lattices of evanescently coupled optical waveguides, is proposed to detect Zak phase difference of photons undergoing Bloch oscillations in topologically distinct Bloch bands of dimerized superlattices. © 2013 Optical Society of America.

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